Apparatus and method for making a double-sided microlens mold and microlens array mold

ABSTRACT

A method for making a double-sided microlens mold and microlens array mold is described which utilizes a spinning half radius diamond cutting member operated in a plunge cut in a technique similar to milling to cut the optical surface into a diamond turnable material. The method can be used to make high sag lens molds with high accuracy. Microlens array molds can be made with a high degree of uniformity and a nearly 100% fill factor.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a divisional of application Ser. No. 09/702,496, filedOct. 31, 2000. The present application is related to U.S. applicationSer. No. 09/702,952, filed Oct. 31, 2000, by John Border, et al., andentitled, “Method Of Manufacturing A Microlens Array Mold And aMicrolens Array;” U.S. application Ser. No. 09/702,362, filed Oct. 31,2000, by John Border, et al., and entitled, “Apparatus For Forming AMicrolens Mold;” U.S. application Ser. No. 09/708,500, Oct. 31, 2000, byJohn Border, et al., and entitled, “Apparatus For Forming A MicrolensArray Mold;” U.S. Pat. No. 6,402,996, issued Jun. 11, 2002, to by JohnBorder, et al., and entitled, “Method Of Manufacturing A Microlens And AMicrolens Array;” U.S. application Ser. No. 09/702,402, filed Oct. 31,2000, by John Border, et al., and entitled, “Method For Making AMicrolens Mold And A Microlens Mold;” and, U.S. application Ser. No.09/702,302, filed Oct. 31, 2000, by John Border, et al., and entitled,“Double-Sided Microlens Array.”

FIELD OF THE INVENTION

[0002] The invention relates generally to the field of improvedmicrolens molds and microlens. More particularly, the invention concernsa method of making a precision mold suitable for forming high quality,micro-sized optical articles, such as a microlens or microlens array.

BACKGROUND OF THE INVENTION

[0003] Rotationally symmetric optical surfaces in molds for injectionmolding or compression molding are typically made either by grinding ordiamond turning. While these techniques work well for larger surfaces,they are not suited for making high quality optical surfaces in smallsizes or arrays. Other techniques are available for making small scalesingle lenses and arrays but they are limited as to fill factor, opticalaccuracy and/or the height or sag of the lens geometry that can be made.

[0004] Grinding relies on an orbital motion of the grinding surfaces tomake a precision optical surface without scratches. However, the orbitalmotion and the grinding surfaces become impractical when making opticalsurfaces below a few millimeters in size. Grinding multiple surfaces foran array can only be done one surface at a time with multiple piecesthat are then fit together.

[0005] Diamond turning can be used to make optical surfaces down to 2millimeters in size but the setup is difficult. Precise location ofmultiple optical surfaces is not possible due to multiple setups. Theneed for multiple setups also increases the machining time for an arrayso that diamond turning becomes cost prohibitive.

[0006] Another technique that is suitable for making microlenses under 2millimeters is polymer reflow. Polymer reflow is done by depositingdrops of polymer onto a surface and then heating the polymer to allow itto melt and reflow into a spherical shape under the influence of surfacetension effects. In order to obtain a truly spherical optical surface,reflow lenses must be separated from one another so that they contactthe underlying surface in a round pattern. To maintain round pattern ofeach lens at the surface, the lenses must be separated from one anotherwhich substantially limits the fill factor in an array. U.S. Pat. No.5,536,455, titled, “Method Of Manufacturing Lens Array,” by Aoyama, etal., Jul. 16, 1996, describes a two step approach for making reflow lensarray with a high fill factor. Using this technique, a second series oflenses is deposited in the gaps between the first set of lenses. Whilethis technique can provide a near 100% fill factor, the second set oflenses does not have round contact with the underlying surface so thatthe optical surface formed is not truly spherical. Also, reflowtechniques in general are limited to less than 100 microns sag due togravity effects. Aspheric surfaces cannot be produced using polymerreflow.

[0007] Grayscale lithography is also useable for making microlensesunder 2 millimeters. Grayscale lithography can be used to make nearlyany shape and high fill factors can be produced in lens arrays. However,reactive ion beam etching and other etching techniques that are used ingray scale lithography are limited as to the depth that can beaccurately produced with an optical surface, typically the sag islimited to under 30 micron.

[0008] High sag lenses are typically associated with high magnificationor high power refractive lenses that are used for imaging. High powerrefractive lenses have tight curvature and steep sides to maximize theincluded angle and associated light gathering or light spreading whichimplies a high sag. In the case of image forming, refractive lenses arepreferred to preserve the wave front of the image. In other cases suchas illumination where the wave front does not have to be preserved,Fresnel or diffractive lenses where the optical curve is cut intosegmented rings, can be used to reduce the overall sag of the lens. Inthe case of microlenses, high power diffractive lenses are not feasibledue to the steepness and narrow spacing of the ring segments at the edgethat would be required to make a low sag, high power microlens.

[0009] U.S. Pat. Nos. 5,519,539, titled, “Microlens Array WithMicrolenses Having Modified Polygon Perimeters,” by Hoopman et al., May21, 1996 and 5,300,263, titled, “Method Of Making A Microlens Array AndMold,” by Hoopman et al., Apr. 5, 1994, describe a method for makinglens arrays that involves casting a polymer into a series of smallreceptacles so that surface tension forms the polymer surfaces intonearly spherical shapes. A correction is done on the shape of thereceptacles to make the surfaces more closely spherical but this resultsin football-shaped intersections so that optical quality and theeffective fill factor are limited.

[0010] Therefore, a need persists in the art for a method of making aprecision microlens mold suitable for forming high quality, micro-sizedoptical articles, such as a microlens or a microlens array.

SUMMARY OF THE INVENTION

[0011] It is, therefore, an object of the invention to provide a methodof making a precision mold for microsized optical articles.

[0012] Another object of the invention is to provide a method of makinga precision mold that does not damage the mold surface.

[0013] Yet another object of the invention is to provide a method ofmaking a mold that utilizes a cutting member that is not limited todepth of penetration.

[0014] Still another object of the invention is to provide a method ofmaking a precision mold that is useable for forming an array ofmicro-sized optical articles.

[0015] It is a feature of the invention that a forming element having ahigh speed, rotatable half-radius diamond cutting member rotatablyengages a substrate in a predetermined cutting pattern to form aprecision mold surface in the substrate.

[0016] According to one aspect of the present invention an apparatus formanufacturing a double-sided microlens, comprises:

[0017] a first mold base and a second mold base, said first mold basehaving a first alignment member for cooperating with correspondinglyaligned second alignment member in said second mold base, and whereineach of said first and said second mold base has a first and secondflexible insert, respectively, for accommodating a pair of juxtaposedmold cavities for receiving a microlens mold in a fixed relationship,and a set of alignment features for aligning said first flexible insertwith said second flexible insert; and,

[0018] a molding assemblage having a first platen and an opposing secondplaten, said first platen supporting said first mold base and saidsecond platen supporting said second mold base for molding adouble-sided microlens in said microlens molds.

[0019] In another aspect of the invention, a method of making adouble-sided microlens, comprising the steps of:

[0020] providing a first mold base and a second mold base each having acorresponding alignment feature and a corresponding insert flexiblymounted in said first mold base and said second mold base, saidcorresponding insert having a corresponding mold cavity and a pair ofalignment features;

[0021] providing corresponding pairs of microlens molds configured forfixed arrangement into said corresponding mold cavity, saidcorresponding mold cavity being formed in a generally polygonalsubstrate;

[0022] arranging each one of said corresponding pairs of microlens moldsinto one of said corresponding mold cavity;

[0023] supportedly arranging said first mold base and said second moldbase on a first platen and an opposed second platen, respectively, of amolding apparatus;

[0024] press closing said first platen upon said opposed second platenof said molding apparatus such that said microlens molds are aligned insaid first mold base and said second mold base; and,

[0025] introducing a molten plastic into said corresponding mold cavity;

[0026] solidifying said molten plastic in said corresponding mold cavityto form a double-sided microlens.

[0027] In another aspect of the invention, a microlens and a microlensarray made by the method of the invention has a spherical shapedsurface, an aspheric shaped surface or an anamorphic shaped surface.

[0028] The present invention has the following advantages: the precisionmicrolens mold can be used to mold high quality, micro-sized opticalarticles, such as microlenses, that have symmetric surfaces with steepsides and high sags; and, the forming element is contoured to producevery accurate optical surfaces in single microlenses or arrays. In thecase of arrays, near 100% fill factor can be achieved in the moldedarticle.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, features, and advantages of thepresent invention will become more apparent when taken in conjunctionwith the following description and drawings wherein identical referencenumerals have been used, where possible, to designate identical featuresthat are common to the figures, and wherein:

[0030]FIG. 1 is a perspective view of the substrate of the inventionhaving a plurality of square microlens mold cavities;

[0031]FIG. 2 is a perspective view of the substrate having a pluralityof hexagonal mold cavities formed by the method of the invention;

[0032]FIG. 3 is a perspective view of the substrate having a pluralityof random mold cavities formed by the method of the invention;

[0033]FIG. 4 is a perspective view of an upright spherical cuttingmember for forming a precision microlens mold;

[0034]FIG. 5 is a perspective view of an aspheric cutting member of theinvention;

[0035]FIG. 6 is a perspective view of the apparatus of the invention forforming a single microlens mold;

[0036]FIG. 7 is a perspective view of the apparatus of the invention forforming a microlens array mold;

[0037]FIG. 8 is an enlarged perspective view of the forming element ofthe invention showing a clearance in mold cavity;

[0038]FIG. 9 is a perspective view of a two-sided microlens mold made bythe method of the invention;

[0039]FIG. 10 is an enlarged perspective view of a microlens array moldmounted for use in a mold base for injection molding or compressionmolding; and,

[0040]FIG. 11 is a perspective view of an apparatus for making adouble-sided microlens.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Turning now to the drawings, and in particular to FIGS. 1-3,improved microlens molds 10, 16, 20 made by the method of the inventionare illustrated. According to FIG. 1, microlens mold 10 has a pluralityof interconnecting square intersection micro-sized mold cavities 12formed in substrate 14, as described more fully below. In FIG. 2,microlens mold 16 has a plurality of interconnecting hexagonal shapedintersection micro-sized mold cavities 18 formed in substrate 14, alsodescribed more fully below. Alternatively, according to FIG. 3,microlens mold 20 has either a single micro-sized mold cavity (notshown) or a plurality of randomly distributed micro-sized mold cavities22 formed in substrate 14, as described below. Substrate 14, in whichthe precision microlens molds 10, 16, 20 of the invention are formed,may be made of any material that is compatible with very hard cuttingtools, such as a diamond milling tool. In the preferred embodiment ofthe invention, substrate 14 includes materials selected from amongcopper, nickel, nickel alloy, nickel plating, brass, and silicon, withhardened nickel plating being most preferred.

[0042] Referring to FIGS. 4 and 5, microlens mold 10, 16, 20 have beendeveloped using the novel diamond milling method of the invention. Asshown in FIG. 4, a spherical forming element 24 having a half radiusdiamond cutting member 26 is used to form the mold cavities 12, 18, 22in the respective substrate 14 of microlens mold 10, 16, 20, by diamondmilling into substrate 14. Diamond cutting member 26 has a substantiallyplanar first face 28, a substantially planar second face 30 orthogonalto and intersecting first face 28, and a spherical contoured shapedcutting face 32 intersecting both the first and second face 28, 30(respectively). First face 28 defines the rotational axis 34 of diamondcutting member 26 when operably connected to control member 36 andaffixed for milling substrate 14, described below. Forming element 24may be used to form a spherical microlens mold 10, 16 or 20 in substrate14 (FIGS. 1-3). Spherical microlens mold 10, 16 or 20 is used for makingspherical microlens articles.

[0043] According to FIG. 5, an alternative aspheric forming element 40has an aspheric diamond cutting member 41. Diamond cutting member 41 hasa substantially planar first face 42, a substantially planar second face46 orthogonal and intersecting first face 42 and an aspheric cuttingface 44 adjoining both first and second face 42, 46 (respectively).First face 42 defines the rotational axis 49 of diamond cutting member41 when operably connected to control member 48 and affixed for millingsubstrate 14, described below. Forming element 40 having control member48 may be used to form an aspheric microlens mold 10, 16 or 20 insubstrate 14 (FIGS. 1-3). Aspheric microlens mold 10, 16 or 20 is usedfor making aspheric microlens articles.

[0044] Referring to FIG. 6, in another aspect of the invention,apparatus 50 for forming a precision single microlens mold (of the typeshown in FIGS. 1-3) for a micro-sized optical article includes a formingelement 24 or 40 operably connected to tool holder 56 and rotatingcontrol member 58. Forming element 24 or 40 has a rotatable hardenedcutting member 26 or 41, preferably diamond (shown clearly in FIGS. 4and 5), fixedly aligned relative to a linearly displaceable (noted byarrow Z) substrate 14. Substrate 14, operably connected to controlmember 64, is arranged for movement towards and away from hardenedcutting member 26 or 41, as described above. Control member 36 or 48,forming element 24 or 40, and control member 64 are preferably all partsof a precision air bearing lathe such as is available from Precitech,Inc., located in Keene, N.H., which is expressly designed for diamondturning of high precision parts. In this embodiment, apparatus 50 canmill a predetermined shaped single microlens mold 52 in the substrate14. Platform 54 is used to provide a solid, non-vibrating base forsupporting apparatus 50 with both forming element 24 or 40 and substrate14 during the mold forming process.

[0045] Referring to FIGS. 6 and 7, substrate 14 is preferably mountedfor movement relative to fixed forming element 24 or 40. According toFIG. 6, apparatus 50 forms a single microlens mold 52 in substrate 14,as discussed above. In FIG. 7, however, apparatus 60 has a substrate 14mounted for three-dimensional movement for forming a microlens moldarray 62. Flexibly moveable substrate 14 is operably connected tocontrol member 64 that governs the movements of substrate 14. Thecontrol member 64 in this case preferably has the ability of precisioncontrolled movement of substrate 14 in the directions X-Y-Z as indicatedin FIG. 7. Precision air bearing lathes with precision X-Y-Z tablemovement are available from Precitech, Inc., located in Keene, N.H. TheX-Y-Z table movement of control member 64 is used to produce theflexible movements of substrate 14 relative to forming element 24 or 40.A tool holder 56 fixedly attached to rotating control member 58, such asthe ones described above, having diamond cutting member 26 or 41 (asdescribed above) is positioned for milling microlens array mold 62 insubstrate 14. By having a movable substrate 14, an array of microlensmold cavities can be formed in substrate 14. Movable substrate 14 isfirst positioned to mill one of a plurality of microlens mold cavities62 a in the microlens array mold 62. After forming the one of aplurality of microlens mold cavities 62 a, forming element 24 or 40 isremoved from the mold cavity 62 a and then the substrate 14 is movedlaterally (X-Y) by control member 64 to another position for forminganother microlens mold cavity 62 b. This procedure is repeated until thedesired number of microlens mold cavities in the microlens array mold 62is formed in substrate 14. Thus, by repeating these steps, apparatus 60having a movable substrate 14 can produce a high quality microlens arraymold 62, such as those illustrated in FIGS. 1-3.

[0046] Those skilled in the art will appreciate that any rotationallysymmetric optical surface, such as a microlens surface, can be producedin the manner described. Spherical surfaces are produced using a halfradius diamond with a circular segment diamond. Aspheres can be producedby using a diamond with an aspheric cutting edge.

[0047] Moreover, some rotationally non-symmetric lens surfaces, such asanamorphic surfaces, can be made using a modified version of thetechnique described. In this case, the diamond tooling is movedlaterally during the cutting action to create an elongated version ofthe spherical or aspheric surface.

[0048] Skilled artisans will appreciate that in order to obtain a highquality lens surface, it is important to follow some basic machiningconcepts. To minimize the center defect in the lens surface produced, itis important to center the diamond cutting member 26 or 41, as shown inFIGS. 4 and 5. The quality of microlens mold 10, 16, 20 is best achievedif the axis of rotation 34 or 49 of diamond cutting member 26 or 41(respectively) is centered to better than 5 microns relative to the axisof rotation (not shown) of the tool holder 56 in rotating control member58 (FIGS. 6 and 7). Also, the tool holder 56 must be balanced toeliminate vibration to minimize chatter. Solid platform 54 helps topromote stability of apparatus 50 and 60 during operation. Further, theright combination of diamond cutting member 26 or 41 rotational speed,feed, i.e., the rate that diamond cutting member 26 or 41 penetratessubstrate 14, and lubrication must be used to obtain the cleanest cut.Moreover, according to FIG. 8, forming element 24 or 40, shown withdiamond cutting member 26 or 41 (similar to those described), must beproduced in such a manner that a sufficient clearance 70 is provided onthe back side 72 of the diamond cutting member 26 or 41 to avoid dragmarks on substrate 14. Drag marks (not shown) typically result frominterference of the backside 72 of diamond cutting member 26 or 41 withthe substrate 14 during the formation of microlens mold 76.

[0049] By using the method of the invention, spherical microlens moldshave been made down to 30 microns in diameter with irregularity ofbetter than 0.50 wave (0.25 micron). Further, microlens mold arrays havebeen made up to 80×80 microlenses with a 250 micron pitch in anorthogonal layout and a near 100% fill factor.

[0050] Moreover, it should be appreciated that the repeated millingprocess of the invention (FIG. 7) is well suited for making accuratemicrolens arrays. Since the process for making each microlens in thearray is unconnected to the other lenses in the array, a nearly 100%fill factor can be obtained in the array.

[0051] Furthermore, aspheric lens surfaces can also be produced usingthis technique. In this case, an aspheric diamond cutting member 41(FIG. 5) is all that is required to make rotationally symmetric asphericlens surfaces. Anamorphic lens surfaces can be made as well using amodified version of this technique. In this case, the same or similardiamond cutting member 41 is moved laterally during the cuttingoperation to produce an elongated lens surface.

[0052] The precision molds 10, 16, 20 (FIGS. 1-3) made with the methodsand apparatus 50 or 60 of the invention, can be used to manufacturelarge numbers of optical articles, such as microlenses. Generally,injection molding and compression molding are the preferred moldingmethods for forming the typically glass or plastic microlenses. In somecases casting is the preferred method.

[0053] Referring to FIGS. 9 and 11, the apparatus used for injectionmolding or compression molding of plastic microlenses using themicrolens molds mounted into a mold base is illustrated. Apparatus formolding a two-sided microlens array 80 is composed of two large blocksor mold bases 82 each having an active molding face 83. Mold bases 82are comprised typically of steel or other metal. Alignment membersarranged on molding faces 83 include guide pins 88, tapered locatingbushings 86 and corresponding apertures (not shown) for receiving guidepins 88 and tapered locating bushings 86. The microlens molds 84 and themold cavities 85 were made according to the methods and apparatus of theinvention. Referring to FIG. 11, in operation, the apparatus 80comprises mold bases 82 which are installed into one of two platens 104,106 of a hydraulic, pneumatic or electrically driven press 108. One sideof the apparatus 80 is connected to one platen 104 of the press 108 andthe other side is connected to the other platen 106. When the presscloses, the guide pins 88 help to align the two sides of the mold base82. At the final closing, the tapered locating bushings 86 align the twosides of the mold base 82 and the microlens molds 84 with each other. Inthe case of molding a two-sided microlens array, it is very importantthat the microlens surfaces on the opposing sides are aligned with eachother. To aid with the alignment of the opposing microlens surfaces ineach of the sides of the mold base 82, the microlens molds 84 aretypically made on square substrates 100 (as shown in FIG. 10) so thatthey cannot rotate in the mold base 82.

[0054] In the case of injection molding, after the press and mold basehave been closed, molten plastic is injected under pressure into themold cavity. After the plastic has cooled in the mold to the point thatit has solidified, the press and mold base are opened and the moldedmicrolens array is removed from the mold.

[0055] In the case of compression molding, prior to the press closing, ahot plastic preform is inserted into the heated mold cavity. The pressand mold base is then closed which compresses the plastic preform andforms the plastic to the shape of the mold cavity and microlens arraymold. The mold and plastic is then cooled, the press and mold base isopened and the molded microlens array is removed from the mold.

[0056] In an alternate case in which a one-sided microlens array orsingle microlens is being injection or compression molded, the opposingside from the microlens mold is typically a plano surface and then,since side-to-side and rotational alignment is not an issue, themicrolens mold may be made onto a round substrate.

[0057]FIG. 10 shows the microlens array mold 96 (also shown in FIG. 9)with a square substrate 100 as is typically used to prevent rotation ofthe microlens array mold surface 98 in the mold base 82 of apparatus 80.The microlens array mold surface 98, the depth of the mold cavity 85 andthe thickness. of the molded microlens array article are determinedprecisely by adjusting the overall height of the substrate 100 and theheight of the larger round substrate 102 on the bottom of the substrate100.

[0058] In cases where casting is the preferred method of production, thematerial is simply poured into the mold cavity and allowed to solidifyby chemical reaction rather than cooling. After the part has solidified,the part is removed from the mold.

[0059] It is our experience that microlens molds made according to theinvention have been used to injection mold microlens surfaces in whichthe sag is not limited, as indicated below. Further, near hemisphericlenses can be produced with very steep sidewalls. Also, it is ourexperience that optical surfaces can be machined directly into moldmaterials such as nickel, copper, aluminum, brass, nickel plating, orsilicon.

[0060] Since apparatus 50, 60 having a forming element 24, 40 withdiamond cutting member 26, 41 (respectively) is quite accurate, it isour experience that lens surfaces can be produced in sizes down to 10micron or less in diameter and 2 micron sag. Lenses up to 25 mm indiameter are also possible with sags of over 12.5 mm.

[0061] The following are several exemplary examples of microlenses madewith the method and apparatus of the invention.

EXAMPLE 1

[0062] A microlens array mold with 80×80 microlenses was made inaluminum. The half radius diamond tool was obtained from ST&F PrecisionTechnologies and Tools, located in Arden, N.C. The microlens surfaceswere 0.250 mm across positioned in a square intersection array. Themicrolenses surfaces were spherical in curvature with a radius of 0.500mm and a sag of 33 micron. Referring to FIG. 4, centering of the diamondcutting member 26 in the control member 36 was done using an iterativeprocess where a test cut was examined under the microscope andadjustments of the location of diamond cutting member 26 were made basedon the size of the center defect. Rotational speed of diamond cuttingmember 26 used was about 1000 rpm. Cutting fluid was purified mineraloil. The result of this process was a center defect of the machined moldof 2 micron and surface irregularity of 1 Wave (0.5 micron). Parts weresubsequently injection molded, using the machined mold surface, toproduce polymethylmethacrylate microlens arrays.

EXAMPLE 2

[0063] Similar to Example 1 with the exception that a hardenednickel-plated substrate was used for the machined mold surface.

EXAMPLE 3

[0064] A microlens array mold with 13×13 microlenses surfaces was madein a hardened nickel-plated substrate. The microlens surfaces were 1.30mm across positioned in a square intersection array. The half radiusdiamond tool was obtained from ST&F Precision Technologies and Tools,located in Arden, N.C. The microlens surfaces were spherical incurvature with a radius of 3.20 mm and a sag of 213 micron. Centeringand the machining process were the same as described in Example 1. Theresult was a center defect of 1.5 micron with a surface irregularity of0.30 Wave (0.15 micron).

EXAMPLE 4

[0065] A series of single microlens surfaces was made in a 715 nickelalloy substrate. The microlens surfaces all were made with a 0.500 mmradius diamond tool. Diameters varied from 0.062 mm to 0.568 mm. Themachining process was similar to that described in Example 1.

EXAMPLE 5

[0066] A larger microlens array of 63.5×88.9 mm was made with 21,760microlenses in total in a 125×175 square intersection array. A diamondhalf radius tool with a 0.5008 mm radius was used, obtained from ChardonTool, Inc., located in Chardon, Ohio. The array was made with a 0.50932pitch and a 0.16609 sag. The substrate was nickel-plated steel. Themachining process was similar to that described in Example 1.

EXAMPLE 6

[0067] It is also within the contemplation of the invention that bymachining matched optical surfaces for a mold, two-sided microlensarrays can be molded in large numbers. According to FIG. 9, two matchedmicrolens array surfaces were made in hardened nickel-plated substrates.The half radius diamond tool or diamond cutting member 26 (FIG. 4) wasobtained from Contour Fine Tooling, Inc., located in Marlborough, N.H.The microlens surfaces were made with a 1.475 mm radius and a 0.750 mmpitch in a square intersection pattern, the sag was 99 micron. Themachining process was similar to that described in Example 1. A centerdefect of 2 micron and an irregularity of 0.3 Wave (0.15 micron) wereachieved in the machined surface. In this case, the two matchedmicrolens array surfaces were mounted in a mold base so that they wereopposed. To align the microlens surfaces on each side, the microlenssurfaces were machined into square substrates prior to mounting into amold base thereby inhibiting rotational misalignment. Taper lockbushings were then used to prevent lateral misalignment. Following thisprocess, two-sided microlens arrays were injection molded frompolymethylmethacrylate. The molded microlenses on the two-sided arraywere aligned with each other within 30 micron.

[0068] The invention has been described with reference to a preferredembodiment. However, it will be appreciated that variations andmodifications can be effected by a person of ordinary skill in the artwithout departing from the scope of the invention.

PARTS LIST

[0069]10 microlens mold with square intersections

[0070]12 mold cavity with square perimeter

[0071]14 substrate

[0072]16 microlens mold with hexagonal intersections

[0073]18 mold cavity with hexagonal perimeter

[0074]20 microlens mold with randomly distributed microlenses

[0075]22 randomly distributed mold cavities

[0076]24 spherical forming element

[0077]26 spherical diamond cutting member

[0078]28 first face of diamond cutting member 26

[0079]30 second face of diamond cutting member 26

[0080]32 spherical contoured cutting face of diamond cutting member 26

[0081]34 rotational axis of diamond cutting member 26

[0082]36 control member for diamond cutting member 26

[0083]40 aspheric forming element

[0084]41 aspheric diamond cutting member

[0085]42 substantially planar first face of aspheric diamond cuttingmember 41

[0086]44 aspheric cutting face of aspheric diamond cutting member 41

[0087]46 substantially planar second face of aspheric diamond cuttingmember 41

[0088]48 control member for diamond cutting member 41

[0089]49 rotational axis of diamond cutting member 41

[0090]50 apparatus for forming a precision single microlens mold

[0091]52 single microlens mold

[0092]54 platform

[0093]56 tool holder for forming element 24 or 40

[0094]58 rotating control member

[0095]60 alternative embodiment of apparatus for making microlens arraymolds

[0096]62 microlens array mold

[0097]62 a single microlens mold cavity

[0098]62 b another single microlens mold cavity

[0099]64 control member

[0100]70 clearance

[0101]72 backside of diamond cutting member

[0102]76 microlens mold apparatus

[0103]80 for molding a two-sided microlens array

[0104]82 mold base

[0105]83 active molding face

[0106]84 microlens molds

[0107]85 mold cavities

[0108]86 tapered locating bushings

[0109]88 guide pins

[0110]96 microlens array mold

[0111]98 microlens array mold surface

[0112]100 square substrate

[0113]102 round substrate

[0114]104 platen

[0115]106 platen

[0116]108 press

What is claimed is:
 1. Method of making a double-sided microlens,comprising the steps of: providing a first mold base and a second moldbase each having a corresponding alignment feature and a correspondinginsert flexibly mounted in said first mold base and said second moldbase, said corresponding insert having a corresponding mold cavity and apair of alignment features; providing corresponding pairs of microlensmolds configured for fixed arrangement into said corresponding moldcavity, said corresponding mold cavity being formed in a generallypolygonal substrate; arranging each one of said corresponding pairs ofmicrolens molds into one of said corresponding mold cavity; supportedlyarranging said first mold base and said second mold base on a firstplaten and an opposed second platen, respectively, of a moldingapparatus; introducing a molten plastic into said corresponding moldcavity; press closing said first platen upon said opposed second platenof said molding apparatus such that said microlens molds are aligned insaid first mold base and said second mold base; and, solidifying saidmolten plastic in said corresponding mold cavity to form a double-sidedmicrolens.
 2. The method recited in claim 1 wherein said step ofproviding corresponding pairs of microlens molds comprise the step offorming each one of said corresponding pairs of microlens molds in saidgenerally polygonal substrate with a diamond cutting member.
 3. Themethod recited in claim 2 wherein said generally polygonal substratecomprises materials selected from the group consisting of: hardenednickel; nickel alloy; brass; copper; aluminum, and silicon.
 4. Themethod recited in claim 2 wherein said generally polygonal substrate ishardened nickel.
 5. The method recited in claim 2 wherein said diamondcutting member has a generally spherical shape.
 6. The method recited inclaim 2 wherein said diamond cutting member has a generally asphericalshape.
 7. The method recited in claim 2 wherein said diamond cuttingmember has an anamorphic shape.